This proposal continues our investigation of fine-structure timing as a stimulus variable affecting auditory perception, especially pitch and timbre perception. Pitch perception is arguably the most crucial perceptual dimension for understanding normal and impaired hearing. We use a class of sounds, which we refer to as regular interval stimuli (RIS) to study the role of temporal fine structure in auditory processing. Our focus is on RIS sounds that do not have period's-repeating temporal structure, e.g., iterated rippled noise (IRN) stimuli. Specific Aim I is to insure that the pitch and timbre of RIS sounds, like IRN stimuli, are based on temporal fine-structure cues. Studies of the resolvability of the spectral structure oflRN stimuli, nonlinear distortion products that may be produced by IRN stimuli, and the role of the envelope oflRN stimuli in pitch and timbre perception will be investigated. Specific Aim 1 is to determine the pitch and timbre of RIS sounds, especially IRN stimuli, when fine-structure temporal regularity exists at more than one regular interval. With few exceptions, the RIS sounds currently used to study the temporal basis for pitch and timbre perception contained a dominant period of temporal regularity. Aim II is to investigate stimuli with several prevalent regular intervals. Specific Aim IlI is to determine if autocorrelation-like models still provide the best temporal-modeling approach for accounting for the pitch and timbre of RIS sounds. To date autocorrelation-like models have done an excellent job of accounting for these perceptions. However, several investigators have challenged the applicability of autocorrelation-like models and several new models have been developed to account for pitch and timbre processing. A goal of Aim m deals with the recent debate about higher order temporal intervals in pitch and timbre perception. Specific Aim IH also deals with RIS sounds that have a pattern of temporal intervals in which the pattern is repeated. It has long been recognized that the pitch-shift of the residue presents a real challenge to models of pitch processing. Thus, Specific Aim HI investigates the pitch-shift of the residue and how various models may account for these pitches. Specific Aim In investigates the integration of information in models across time within a spectral channel, and especially, across spectral channels.